Frequency translation module frequency limiting amplifier

ABSTRACT

A system for processing signal communications between a frequency translation module and an integrated receiver decoder. According to an exemplary embodiment, the decoder and the frequency translation module comprise a signal processing apparatus comprising an input for receiving an frequency shift keyed modulated signal, an amplifier having negative feedback coupled to said input, wherein said input is further coupled to a first source of reference potential and a second source of reference potential; and a tank circuit coupled between said differential amplifier and an output. More particularly, the amplifier may comprise a first transistor having a first collector, a first emitter and a first base coupled to a signal source wherein said first base is further coupled to said first collector and a second transistor with a second base, a second emitter coupled to said first emitter, and a second collector, wherein said second collector is coupled to a bandpass filter and said bandpass filter is further coupled to an output.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit, under 35 U.S.C. §365 ofInternational Application PCT/US07/006299, filed on Mar. 13, 2007, whichwas published in accordance with PCT Article 21 (2) on Nov. 8, 2007, inEnglish and which claims the benefit of U.S. Provisional PatentApplication No. 60/787,072, filed on Mar. 29, 2006, in English.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to signal communications, andmore particularly, to an architecture and protocol for processing signalcommunications between a frequency translation apparatus, which may bereferred to herein as a frequency translation module (FTM), and anintegrated receiver-decoder (IRD).

2. Background Information

In a satellite broadcast system, one or more satellites receive signalsincluding audio and/or video signals from one or more earth-basedtransmitters. The satellite(s) amplify and rebroadcast these signals tosignal receiving equipment at the dwellings of consumers viatransponders that operate at specified frequencies and have prescribedbandwidths. Such a system includes an uplink transmitting portion (i.e.,earth to satellite(s)), an earth-orbiting satellite receiving andtransmitting portion, and a downlink portion (i.e., satellite(s) toearth).

In dwellings that receive signals from a satellite broadcast system,signal receiving equipment may be used to frequency shift the entirebroadcast spectrum of the satellite(s), and frequency stack theresultant output onto a single coaxial cable. That is, the frequencyspectrum associated with one set of signals is shifted to thefrequencies adjacent to, or different from, the frequency spectrum ofanother set of signals, thereby positioning or stacking the sets ofsignals in the frequency domain. As the number of satellites within asatellite broadcast system increases, and with the proliferation of highdefinition satellite channels, a point will be reached where the totalbandwidth required to accommodate all of the satellites will exceed thetransmission capability of the coaxial cable. It has become necessaryfor the satellite decoder industry to implement more satellite slotsinto their distribution systems. To provide for the increased number ofsatellite slot transmissions a more elaborate means for satelliteconfigurations selection has been developed called the frequencytranslation module (FTM) method.

An FTM for delivering satellite signals to Integrated Receiver Decoders(IRDs) comprises one or more input/outputs (I/Os) coupled to low noiseblock amplifiers (LNB), and one or more input/outputs coupled to IRDs.The FTM module operative to receive requests from the IRD indicatingdesired satellite program channels. In response to the request from theIRD, the FTM module controls the appropriate LNB such that the requestedchannel, or block of channels is delivered to the FTM IO. The FTM modulethen may frequency shift the requested channel to a second frequencycorresponding to an unoccupied frequency on the transmission line to theIRDs. The FTM module zo then communicates to the requesting IRD thefrequency on which the requested channel is being supplied. When the FTMis operative to couple a plurality of satellite program channels to aplurality of IRDs, the FTM individually commands each LNB to supply thedesired channels or band of channels, and outputs each of the desiredchannels or band of channels on the same transmission line to the IRDs,with each desired channel or band of channels modulated at uniquefrequencies.

The FTM uses a UART controlled 2.3 MHz, Frequency Shift Key (FSK)modulation scheme to communicate selection commands to the IRDs and theFTM. Present day satellite decoder systems use complicated PLL andsuperhetrodyne receivers to amplify the narrow band required for FSKreception with no conversion or detection. This results in anundesirably expensive implementation that must be implemented in eachIRD and FTM, the cost being far more than the cost of the legacy DiSEqCcommunication system. There is a need for a low cost FSK signalprocessing means with frequency filter, amplitude limiting, and widedynamic range without the need for an expensive AGC system. The presentinvention described herein addresses this and/or other problems.

SUMMARY OF THE INVENTION

In accordance with an aspect of the present invention, an apparatus forprocessing an FSK signal is disclosed. According to an exemplaryembodiment, the apparatus comprises an input for receiving an frequencyshift keyed modulated signal, an amplifier having negative feedbackcoupled to said input, wherein said input is further coupled to a firstsource of reference potential and a second source of referencepotential; and a tank circuit coupled between said differentialamplifier and an output.

In accordance with another aspect of the present invention, an FSKsignal processing apparatus is disclosed. According to an exemplaryembodiment, the FSK signal processing apparatus comprises a firsttransistor having a first collector, a first emitter and a first basecoupled to a signal source wherein said first base is further coupled tosaid first collector; and a second transistor with a second base, asecond emitter coupled to said first emitter, and a second collector,wherein said second collector is coupled to a bandpass filter and saidbandpass filter is further coupled to an output.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention,and the manner of attaining them, will become more apparent and theinvention will be better understood by reference to the followingdescription of embodiments of the invention taken in conjunction withthe accompanying drawings, wherein:

FIG. 1 is a diagram showing an exemplary environment for implementingthe present invention.

FIG. 2 is a block diagram showing further details of the FTM of FIG. 1according to an exemplary embodiment of the present invention.

FIG. 3 is a diagram showing further details of the interconnectivitybetween the FTM 20 and IRD 60 of FIG. 1 according to an exemplaryembodiment of the present invention.

FIG. 4 is a diagram of an exemplary embodiment for implementing thepresent invention showing further details of the transceiver 32 of FIG.3.

FIG. 5 is a diagram of an exemplary embodiment for implementing thepresent invention showing further details of the frequency selection andpreprocessing circuitry 321 of FIG. 4.

FIG. 6 is a diagram of an exemplary embodiment for implementing thepresent invention showing further details the amplification and dataclamp circuitry 325 of FIG. 4.

The exemplifications set out herein illustrate preferred embodiments ofthe invention, and such exemplifications are not to be construed aslimiting the scope of the invention in any manner.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

It is desirable to disconnect the low impedance LNB power supply outputimpedance from the FTM circuits when in the FTM mode by effectivelyraising the LNB power supply output impedance when in the FTM mode. As avoltage source, conventional LNB power supplies represent a lowimpedance to ground. This low impedance, if uninterrupted, overloads themodulated 2.3 MHz FTM signal causing waveform distortion. An aspect ofthe present invention involves disconnecting a low impedance output ofan LNB power supply from a communication network, such as a 2.3 MHzcommunication network.

Referring now to the drawings, and more particularly to FIG. 1, adiagram of an exemplary embodiment 100 for implementing the presentinvention is shown. Embodiment 100 of FIG. 1 comprises a plurality ofsignal receiving means such as signal receiving elements or devices 10,such as parabolic antennas in is exemplary embodiment of the invention,frequency translating means such as FTM 20, a plurality of signalsplitting means such as signal splitters 40, and a plurality of signalreceiving and decoding means such as IRDs 60. According to an exemplaryembodiment described herein, the aforementioned elements of embodiment100 are operatively coupled to one another via a transmission mediumsuch as coaxial cable, although other types of transmission mediums mayalso be used according to the present invention. Embodiment 100 may forexample represent a signal communication network within a givenhousehold and/or business.

Signal receiving elements 10 are each operative to receive signalsincluding audio, video, and/or data signals (e.g., television signals,etc.) from one or more signal sources, such as a satellite broadcastsystem and/or other type of signal broadcast system. According to anexemplary embodiment, signal receiving element 10 is embodied as anantenna such as a satellite receiving dish, but may also be embodied asany type of signal receiving element.

FTM 20 is operative to receive signals including audio, video, and/ordata signals (e.g., television signals, etc.) from signal receivingelements 10, and process the received signals using functions includingsignal tuning and frequency translation functions to generatecorresponding output signals that are provided to IRDs 60 via coaxialcable and signal splitters 40. According to an exemplary embodiment, FTM20 may communicate with a plurality IRDs 60 within a system. Forpurposes of example and explanation, however, FIG. 1 shows FTM 20connected to 8 IRDs 60 using simple two-way signal splitters 40. Furtherexemplary details regarding FTM 20, and its ability to communicate withIRDs 60 will be provided later herein.

Signal splitters 40 are each operative to perform a signal splittingand/or repeating function. According to an exemplary embodiment, signalsplitters 40 are each operative to perform a 2-way signal splittingfunction to facilitate signal communication between FTM 20 and IRDs 60.

IRDs 60 are each operative to perform various signal receiving andprocessing functions including signal tuning, demodulation and decodingfunctions. According to an exemplary embodiment, each IRD 60 isoperative to tune, demodulate and decode signals provided from FTM 20via signal splitters 40, and enable aural and/or visual outputscorresponding to the received signals. As will be described laterherein, such signals are provided from FTM 20 to IRDs 60 responsive torequest commands from IRDs 60, and such request commands may eachrepresent a request for a desired band of television signals. With asatellite broadcast system, each request command may for exampleindicate a desired satellite and/or a desired transponder. The requestcommands may be generated by IRDs 60 responsive to user inputs (e.g.,via remote control devices, etc.).

According to an exemplary embodiment, each IRD 60 also includes anassociated audio and/or video output device such as astandard-definition (SD) and/or high-definition (HD) display device.Such display device may be integrated or non-integrated. Accordingly,each IRD 60 may be embodied as a device such as a television set,computer or monitor that includes an integrated display device, or adevice such as a set-top box, video cassette recorder (VCR), digitalversatile disk (DVD) player, video game box, personal video recorders(PVR), computer or other device that may not include an integrateddisplay device.

Referring to FIG. 2, a block diagram providing further details of FTM 20of FIG. 1 according to an exemplary embodiment of the present inventionis shown. FTM of FIG. 2 comprises switching means such as cross overswitch 22, a plurality of tuning means such as tuners 24, a plurality offrequency converting means such as frequency up converters (UCs) 26, aplurality of amplifying means such as variable gain amplifiers 28,signal combining means such as signal combiner 30, transceiving meanssuch as transceiver 32, and control means such as controller 34. Theforegoing elements of FTM 20 may be implemented using integratedcircuits (ICs), and one or more elements may be included on a given IC.Moreover, a given element may be included on more than one IC. Forclarity of description, certain conventional elements associated withFTM 20 such as certain control signals, power signals and/or otherelements may not be shown in FIG. 2.

Cross over switch 22 is operative to receive a plurality of inputsignals from signal receiving elements 10. According to an exemplaryembodiment, such input signals represent various bands of radiofrequency (RF) television signals. With a satellite broadcast system,such input signals may for example represent L-band signals, and crossover switch 22 may include an input for each signal polarization usedwithin the system. Also according to an exemplary embodiment, cross overswitch 22 selectively passes the RF signals from its inputs to specificdesignated tuners 24 responsive to control signals from controller 34.

Tuners 24 are each operative to perform a signal tuning functionresponsive to a control signal from controller 34. According to anexemplary embodiment, each tuner 24 receives an RF signal from crossover switch 22, and performs the signal tuning function by filtering andfrequency down is converting (i.e., single or multiple stage downconversion) the RF signal to thereby generate an intermediate frequency(IF) signal. The RF and IF signals may include audio, video and/or datacontent (e.g., television signals, etc.), and may be of an analog signalstandard (e.g., NTSC, PAL, SECAM, etc.) and/or a digital signal standard(e.g., ATSC, QAM, QPSK, etc.).

Frequency up converters (UCs) 26 are each operative to perform afrequency translation function. According to an exemplary embodiment,each frequency up converter (UC) 26 includes a mixing element and alocal oscillator (not shown in FIGS.) that frequency up converts an IFsignal provided from a corresponding tuner 24 to a designated frequencyband responsive to a control signal from controller 34 to therebygenerate a frequency up converted signal.

Variable gain amplifiers 28 are each operative to perform a signalamplification function. According to an exemplary embodiment, eachvariable gain amplifier 28 is operative to amplify a frequency convertedsignal output from a corresponding frequency up converter (UC) 26 tothereby generate an amplified signal. Although not expressly shown inFIG. 2, the gain of each variable gain amplifier 28 may be controlledvia a control signal from controller 34.

Signal combiner 30 is operative to perform a signal combining (i.e.,summing) function. According to an exemplary embodiment, signal combiner30 combines the amplified signals provided from variable gain amplifiers28 and outputs the resultant signals onto a transmission medium such ascoaxial cable for transmission to one or more IRDs 60 via signalsplitters 40.

Transceiver 32 is operative to enable communications between FTM 20 andIRDs 60. According to an exemplary embodiment, transceiver 32 receivesvarious signals from IRDs 60 and relays those signals to controller 34.Conversely, transceiver 32 receives signals from controller 34 andrelays those signals to one or more IRDs 60 via signal splitters 40.Transceiver 32 is may for example be operative to receive and transmitsignals in one or more predefined frequency bands. Further exemplarydetails regarding transceiver 32, and its operation will be providedlater herein.

Controller 34 is operative to perform various control functions.According to an exemplary embodiment, controller 34 receives requestcommands for desired bands of television signals from IRDs 60. As willbe described later herein, each IRD 60 may transmit its request commandto FTM 20 during a separate time slot that is assigned by controller 34.With a satellite broadcast system, a request command may indicate adesired satellite and/or a desired transponder that provides a desiredband of television signals. Controller 34 enables signals correspondingto the desired bands of television signals to be transmitted tocorresponding IRDs 60 responsive to the request commands.

According to an exemplary embodiment, controller 34 provides variouscontrol signals to cross over switch 22, tuners 24, and frequency upconverters (UCs) 26 that cause the signals corresponding to the desiredbands of television signals to be transmitted to IRDs 60 via atransmission medium such as coaxial cable. Controller 34 also providesacknowledgement responses to IRDs 60 responsive to the request commandswhich indicate the frequency bands (e.g., on the coaxial cable, etc.)that will be used to transmit the signals corresponding to the desiredbands of television signals to IRDs 60. In this manner, controller 34may allocate the available frequency spectrum of the transmission medium(e.g., coaxial cable, etc.) so that all IRDs 60 can receive desiredsignals simultaneously.

Referring to FIG. 3, a diagram of an exemplary embodiment 300 forimplementing aspects of the present invention, shows further details ofthe interconnectivity between the FTM 20 and IRD 60 of FIG. 1.Embodiment 300 of FIG. 3 comprises a protection circuit 31, atransceiver 32, and a signal combiner 30 within the FTM 20. Within theIRD 60, a tuner 36, a transceiver 37, an LNB power supply 38, a DiSEqCencoder/decoder 39, a switch 33, and a protection circuit 35 are shown.

Protection circuit 31 is operative to pass desired signals, such as FTMcontrol signals and television signals without distortion whileprotecting the FTM circuitry from lightning surge and otherenvironmental electrical disturbances. According to an exemplaryembodiment, protection circuit 31 comprises devices such as surgeprotection diodes implemented to absorb energy from positive andnegative lightning surge events. The surge protection diodes areconfigured not to present a non-linear conduction path to the 2.3 MHzFTM signal.

Signal combiner 30 is operative to perform a signal combining (i.e.,summing) function. According to an exemplary embodiment, signal combiner30 combines the amplified signals provided from variable gain amplifiers28 and outputs the resultant signals onto a transmission medium such ascoaxial cable for transmission to one or more IRDs 60 via signalsplitters 40.

Transceiver 32 is operative to enable communications between FTM 20 andIRDs 60. According to an exemplary embodiment, transceiver 32 receivesvarious signals from IRDs 60 and relays those signals to controller 34.Conversely, transceiver 32 receives signals from controller 34 andrelays those signals to one or more IRDs 60 via signal splitters 40.Transceiver 32 may for example be operative to receive and transmitsignals in one or more predefined frequency bands. Further exemplarydetails regarding transceiver 32, and its operation will be providedlater herein.

Similarly to protection circuit 31, protection circuit 35 is operativeto pass desired signals, such as FTM control signals and televisionsignals without distortion while protecting the IRD 60 circuitry fromlightning surge and other environmental electrical disturbances.According to an exemplary embodiment, protection circuit 35 comprisessurge protection diodes implemented to absorb energy from positive andnegative lightning surge events. The surge protection diodes areconfigured not to present a non-linear conduction path to the 2.3 MHzFTM signal or the incoming television signals transmitted from the FTM20.

Tuner 36 is operative to perform a signal tuning function responsive toa control signal from IRD controller in response to a channel selectionfrom the user. According to an exemplary embodiment, the tuner receivesan RF signal from protection circuit 35, and performs the signal tuningfunction by filtering and frequency down converting (i.e., single ormultiple stage down conversion) the RF signal to thereby generate anintermediate frequency (IF) signal. The RF and IF signals may includeaudio, video and/or data content (e.g., television signals, etc.), andmay be of an analog signal standard (e.g., NTSC, PAL, SECAM, etc.)and/or a digital signal standard (e.g., ATSC, QAM, QPSK, etc.).

Transceiver 37 is operative to enable communications between FTM 20 andIRDs 60. According to an exemplary embodiment, transceiver 37 receivesvarious signals from FTM 20 and relays those signals to the IRDcontroller. Conversely, transceiver 37 receives signals from IRDcontroller and relays those signals to the FTM via coaxial cable andprotection circuits 31 and 35. Transceiver 37 may for example beoperative to receive and transmit signals in one or more predefinedfrequency bands. Further exemplary details regarding transceiver 37, andits operation will be provided later herein through the exemplarydescription of transceiver 32, which operates and communicates in asubstantially similar manner to transceiver 37.

The LNB power supply 38 is operative to generate the required operatingDC power for the LNBs when the system is operating in Legacy LNB mode.In Legacy more, the LNB is operative to receive communications from theset top box via pulsed tones coupled to the LNB power supply lines.According to an exemplary embodiment, the LNB power supply 38 is a toconventional LNB power supply comprising a DC to DC, Boost switchingpower supply, with the ability to power down or disable the output. TheLNB power supply comprises a linear regulator which can superimpose a 22kHz tone onto the DC output voltage. The output of the linear regulatoris typically a push-pull type, but can equally be other configurations,such as emitter is follower type output.

The switch 33 is operative to couple the LNB power supply 38 to theprotection circuit 35 with a low impedance when the IRD 60 is operatingin the Legacy mode. The switch 33 decouples the LNB power supply 38 fromthe protection circuit 35 with a high impedance when the IRD 60 isoperating in the FTM mode.

The DiSEqC encoder and decoder 39 is operative to generate the requiredcontrol tones to communicate to the LNBs when the IRD is operating inthe Legacy mode. According to an exemplary embodiment, there are two 22kHz tone modes, constant tone and two-way pulse width modulated (PWM)tone control mode. When the LNB regulator is transmitting tone, theDiSEqC encoder and decoder 39 provides a low impedance output to theswitch 33.

FIG. 4 is a diagram of an exemplary embodiment for implementing thepresent invention showing further details the transceiver 32 of FIG. 3.While reference is made to the transceiver 32 of the FTM 20 of FIG. 3 inthis exemplary embodiment, the transceiver and the described circuitrycan equally be implemented in the IRD 60. The transceiver of environment32 comprises frequency selection and preprocessing circuitry 321, ademodulator 323, amplification and data clamp circuitry 325, and a dataslicer 327. The transceiver of environment 32 comprises frequencyselection and preprocessing circuitry 321, a demodulator 323,amplification and data clamp circuitry 325, and a data slicer 327.

The frequency selection and preprocessing circuitry 321 is operative toreceive the 2.3 MHz FSK FTM control signals from an FTM control modulevia the transmission line. The frequency selection and preprocessingcircuitry 321 prefilters the received FSK to signal to remove unwantedspurious and adjacent channel signals present at nearby frequencies. Thefrequency selection and preprocessing circuitry 321 the amplifies orattenuates the received signal such that the amplitude of the receivedsignal is within a is predetermined range such that it is suitable forcoupling to the demodulator 323. Further exemplary details of thefrequency selection and preprocessing circuitry 321, and its operationwill be provided later herein

The demodulator 323 is operative to receive the filtered and amplitudeadjusted FSK FTM control signals from the frequency selection andpreprocessing circuitry 321. The demodulator 323 converts the frequencyshift keyed digitally modulated RF signal into a binary baseband signalsuitable for further digital processing. The demodulator may accomplishthis objective by stripping a portion of the 2.3 MHZ carrier signal fromthe FSK FTM control signal to extract the two discrete frequencies thatcomprise the binary data present in the FSK signal. The demodulator 323then designates one frequency as the “mark” frequency and the other asthe “space” frequency. The mark and space correspond to binary one andzero, respectively. By convention, mark corresponds to the higher radiofrequency. The binary signal is then passed to the amplification anddata clamp circuitry 325.

The amplification and data clamp circuitry 325 is operative to prefilterthe received binary signal to remove unwanted spurious noise and tocondition the signal to minimize bit errors and maximize signal quality.The amplification and data clamp circuit 325 amplifies or attenuates thereceived binary signal such that the amplitude of the binary signal iswithin a predetermined range such that it is suitable for coupling tothe data slicer 327. Further exemplary details amplification and dataclamp circuitry 325, and its operation will be provided later herein.

The data slicer 327, sometimes called a zero threshold crossingdetector, comprises circuitry used to detect and indicate instances whenan input signal crosses a predetermined threshold, such as the 0 voltlevel. An exemplary embodiment of this circuit is an operationalamplifier with the input signal applied to the positive input and thenegative input grounded. The resulting signal output from the operationamplifier will have a positive value when the input voltage is positive,and when the input voltage is negative, the output voltage is a negativevalue. The magnitude of the output voltage is a property of theoperational amplifier and its power supply. Another exemplary embodimentof a data slicer feeds the input signal into both the positive terminalof the operational amplifier and into a threshold detector, thethreshold detector generates a middle or average voltage level for thebaseband signal. The output of the threshold detector is then fed to thenegative terminal of the operational amplifier. The operationalamplifier output is then a positive value when the input signal ishigher than the average voltage level for the baseband signal, ornegative when the input signal is lower than the average level for thebaseband signal. Again, the magnitude of the output voltage is aproperty of the operational amplifier and its power supply. The outputof the data slicer 327 is then applied to the microprocessor.

FIG. 5 is a diagram of an exemplary embodiment for implementing anaspect of the present invention showing further details the frequencyselection and preprocessing circuitry 321 of FIG. 4. The frequencyselection and preprocessing circuitry 321 comprises differentialamplifier comprising a first transistor configured as an emitterfollower T41 and a second transistor configured as common base amplifierT42. The emitter follower T41 offers a high input impedance and hasnegative feedback through resistor R41. Resistors R43, R41, and R42create a voltage divider circuit for regulating the voltage provided bythe first voltage supply V41 and the input FSK signal IN at the base andto the collector of the emitter follower T41. The negative feedbackthrough resistor R41 keeps the circuit from oscillation and limits theinput signal coupling to the common base amplifier T42 to the voltagesupplied by the first voltage supply V41. The minimum voltage suppliedto the base of the emitter follower T41 is limited to the voltagegenerated across resistor R42. Capacitor C41 couples the input FSKsignal IN to the base of the emitter follower T41 as well as limitingunwanted dc bias generated outside of the frequency selection andpreprocessing circuitry 321.

A third voltage source biases the base of the common base amplifier T42through resistors R48 and R45 configured as a voltage dividers andcapacitor C42. This common base amplifier configuration is useful forhigh frequency applications because the base separates the input andoutput, minimizing oscillations at high frequency. It has a high voltagegain, relatively low input impedance and high output impedance comparedto the common collector configuration. Resistors R46 and R44 divide thevoltage supplied by a second voltage source V42.

Inductor L41 and capacitor C43 are configured in a parallel circuitcreating a tank circuit tuned to the center frequency of the FSKtransmission. A dequeing resistor R47 is used to widen the bandwidth andgives a load to the common base amplifier T42. The output of the tankcircuit is then output to the demodulator 323 of FIG. 4.

FIG. 6 is a diagram of an exemplary embodiment for implementing thepresent invention showing further details of the amplification and dataclamp circuitry 325 of FIG. 4. The amplification and data clampcircuitry 325 receives a binary signal representing FTM control signalsfrom the demodulator 323 of FIG. 4. The amplification and data clampcircuitry 325 then amplifies or attenuates the received binary signalsuch that the amplitude of the binary signal is within a predeterminedrange such that it is suitable for coupling to the data slicer 327 ofFIG. 4. In an exemplary embodiment according to the present invention,the amplification stage is configured as an inverting amplifier.Resistors R53 and R54 are configured as a voltage divider to generatethe desired DC voltage at the positive terminal of operational amplifierA51. Capacitor C52 is operative to decouple and unwanted or spurioushigher frequency signals from the positive terminal of operationalamplifier A51. The values of resistors R51 and R52 are used to determinethe overall gain of the amplification stage such that the gain is equalto the negative of R52 divided by R51. Capacitor C51 is operative tofrequency limit the received binary signal. Decoupling capacitor C53 isoperative to reduce unwanted noise and spurious signals from exiting theamplification stage. The gain of the amplification stage is optimallyconfigured such that the minimum amplitude deviation expected from thedemodulator 325 of FIG. 4 causes the NPN transistor T51 and the PNPtransistor T52 clamps to operate. At greater deviation levels the clampwill always be on. Resistors R55 and capacitor C54 couple the amplifiedbinary signal from the amplification stage to the data clamping stage.R55 is further operable as a current limiting resistor to insure theamplification stage is not over stressed or to ensure that distortion isnot introduced into the output waveform.

The PNP transistor T52 and NPN transistor T52 are configured as a dataclamp circuit. The PNP transistor T52 clamps the output voltage from anamplification stage to a first fixed level once the binary signal dropsbelow a predetermined threshold value. This threshold value isdetermined by the DC value of the second voltage supply V52 andresistors R57 and R58 configured as a voltage divider. Once the binarysignal level drops to a level less than the base voltage of the PNPtransistor and the voltage drop from the base to the collector, commonly0.7 volts for silicon construction, the output voltage will be clampedto the first fixed level. When the binary signal level rises to a levelhigher than the base voltage of the NPN transistor plus the voltage dropfrom the base to the emitter the output voltage will be clamped to thesecond fixed level. The resulting waveform is clamped to fixedpredetermined levels on all cycles of the waveform and therefore has thedesirable result of maintaining a fixed signal level on the outputsignal. This enhances signal quality and reduces error in the dataslicer 327 of FIG. 4 and in the microprocessor. The microprocessor maybe implemented using a digital signal processor or a universalasynchronous receiver-transmitter (UART) A UART receives data in asequential fashion and assembles the bits into complete bytes.

As described herein, the present invention provides an architecture andprotocol for enabling signal communications between an FTM and an IRD.While this invention has been described as having a preferred design,the present invention can be further modified within the spirit andscope of this disclosure. The description herein is therefore intendedto cover any variations, uses, or adaptations of the invention using itsgeneral principles. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains and which fallwithin the limits of the appended claims.

The invention claimed is:
 1. An apparatus comprising: an input pointreceiving a frequency shift keyed (FSK) modulated signal; an outputpoint; a differential amplifier coupled between said input and outputpoints operative to amplify said FSK modulated signal, said differentialamplifier including a pair of first and second transistors, said firsttransistor being configured as an emitter follower and said secondtransistor being configured as a common-base amplifier, said firsttransistor having a first collector, a first base, and a first emitter,said second transistor having a second collector, a second base, and asecond emitter, said first base coupled to said input point; a band-passfilter coupled between said second collector and said output, saidband-pass filter being tuned to substantially a center frequency of saidFSK modulated signal; a negative feedback path coupled between saidfirst collector and said first base; a first voltage divider coupledbetween first and second sources of reference potential operative toenable to regulate a voltage provided by said first source of referencepotential and said FSK signal at said first base, said first voltagedivider coupled to said first base; a capacitor coupled between saidinput point and said first base; and a bias circuit including a secondvoltage divider coupled between third and fourth sources of referencepotential operative to enable to bias said second base.
 2. The apparatusof claim 1 wherein said bias circuit includes a capacitor coupledbetween said second base and said fourth source of reference potential.3. The apparatus of claim 1 wherein said band-pass filter includes aresistor operative to enable to widen a bandwidth of said band-passfilter and to provide a load to said common-base amplifier.
 4. Anapparatus comprising: means for receiving a frequency shift keyed (FSK)modulated signal; means for providing an output signal; means includinga differential amplifier for amplifying said FSK modulated signalcoupled between said receiving means and said output means, saiddifferential amplifier including a pair of first and second transistors,said first transistor being configured as an emitter follower and saidsecond transistor being configured as a common-base amplifier, saidfirst transistor having a first collector, a first base, and a firstemitter, said second transistor having a second collector, a secondbase, and a second emitter, said first base coupled to said receivingmeans; means coupled between said second collector and said output meansfor band-pass filtering an output signal of said amplifying means, saidband-pass filtering means being tuned to substantially a centerfrequency of said FSK modulated signal; means coupled between said firstcollector and said first base for providing a negative feedback; meansincluding a resistor coupled between first and second sources ofreference potential for regulating a voltage provided by said firstsource of reference potential and said FSK signal at said first base,said voltage regulating means coupled to said first base; meansincluding a capacitor for AC coupling said receiving means and saidfirst base; and means including a resistor coupled between said thirdand fourth sources of reference potential for biasing said second base.5. The apparatus of claim 4 wherein said biasing means includes acapacitor for providing an AC path between said second base and saidfourth source of reference potential.
 6. The apparatus of claim 4wherein said band-pass filtering means includes a resistor for wideninga bandwidth of said band-pass filtering means and for providing a loadto said common-base amplifier.